A new study of several major European cities says that one key to cutting car emissions is eliminating parking options for drivers. Simple.

According to findings in a new paper (PDF) from the Institute for Transportation and Development Policy, Europe's Parking U-Turn, several major European cities have had tremendous success regulating car emissions simply by eliminating the places in which cars can be parked.

Hamburg, Zurich, Paris, and London have all cut parking spots, lessening auto emissions as well as spurring residents to seek out alternative transportation methods, like walking or biking.

Hamburg and Zurich used a cap-and-trade approach to decrease parking, wherein every off-street parking spot built was balanced by an on-street spot being converted to a park or community space. Paris, on the other hand, took a more direct approach: The French capital spent about $20 million on bollards to block cars from using existing parking spots.

GOOD has in the past covered legislation confronting the artificially lowpricing of parking — including San Francisco's supply-and-demand meters— but this is the first time we've heard of cities outright destroying parking spots. Several cities in the study also did away with minimum parking standards for new residential and commercial developments (an idea attached to a California parking bill last year that was eventually amended beyond recognition).

Regardless of methodology, the results were impressive:

Take Amsterdam, a city that saw a 20 percent reduction in car traffic in the inner city, as well as a 20 percent decrease in traffic searching for a place to park, since strict parking enforcements were implemented. In Copenhagen, Denmark, traffic dropped by 6 percent in five years, despite a 13 percent increase in car ownership over the same period.

The logic is simple: Less room for cars equals fewer cars equals cleaner air. The end.